In a liquid crystal display (LCD), a polarizing plate is used to control optical rotation of beams that pass through liquid crystals. Conventionally, in such a polarizing plate, a polarizer obtained by dying a resin film, such as a polyvinyl alcohol or the like with iodine or a dichromatic dye and stretching the film in one direction has been widely used. However, there has been a problem that the aforementioned polarizers are poor in heat resistance and light resistance depending on the kind of the dye or the resin film. Moreover, film manufacturing equipment has become bigger as liquid crystal panels become bigger, which has become a problem.
In contrast, a method for forming a polarizing film by coating a coating solution containing a lyotropic liquid crystal compound on a substrate, such as a glass plate or a resin film and the like to orient the lyotropic liquid crystal compound is known. The lyotropic liquid crystal compound forms supramolecular aggregates exhibiting liquid crystallinity in the solution, so that the long axis direction of the supramolecular aggregates is oriented in a flowing direction when flowing after applying shearing stress onto the coating solution containing this. Examples of such lytropic liquid crystal compounds include azo-base compounds (JP 2006-323377 A). Lyotropic liquid crystal compounds based polarizing films do not need to be stretched and are easy to have a greater thickness because of no shrinkage in a width direction by stretching. Further, the lyotropic liquid crystal compounds based polarizing films are expected to have potential because the thickness can be reduced significantly.
To improve quality of the polarizing films, the polarizing film preferably exhibits large absorption dichroism at a wavelength of 520 to 600 nm in the wavelength range having high visibility in which human's eyes feel most strongly. Conventional azo compounds, however, mostly have a maximum absorption wavelength on a long-wavelength side in a visible light region, resulting in a problem of low-quality polarizing films. Thus, a novel azo compound which has resolved this problem has been demanded.